Control and measurement of flow of fluids, both gases and liquids, has presented considerable problems to the prior art, particularly at extremely low flow rates. Typically, prior art systems for use at low to moderate flow rates, e.g. rates of 1 cm.sup.3 /hr. to 1000 cm.sup.3 /hr. have proven to be either relatively inaccurate or fairly expensive in terms of having an accurate measuring system. Typical of known devices for this purpose are orifice or capillary meters connected to differential pressure transmitters, or, for larger flows, turbine meters.
The present invention teaches means for readily indicating flow rates of gases or liquids with a high degree of accuracy over a very wide range of flow rates by a relatively simple and inexpensive system. It can be automated to the point of adjusting flow conditions responsive to the measurement it obtains of fluid flow, and/or setting off suitable warning devices or the like when flow is above or below desired levels. The present system, which may use a glass or ceramic coated iron float in a quartz tube, can be used in very corrosive environments and/or at high temperatures. Due to its ability to inexpensively measure fluid flow at low flow rate, e.g. 5 cm.sup.3 /hr. to 1000 cm.sup.3 /hr., it offers the possibility of being used for intravenous flow control as described in U.S. Pat. No. 3,605,741, the general portions of which relating to intravenous flow being incorporated by reference herewith.